TW202433197A - Mirror arrangement for absorbing radiation, and lithography system - Google Patents

Abstract

The invention relates to a mirror arrangement, in particular for a lithography system (1), comprising: a plurality of mirror elements (23) for reflecting radiation (16), a plurality of carrier elements (24), which each carry one of the mirror elements (23), and a mount arrangement (25) having insert openings (26) formed in each case to accommodate a respective one of the carrier elements (24), with the plurality of carrier elements (24), which each carry one of the mirror elements (23), being accommodated in the insert openings (26) of the mount arrangement (25). For absorbing radiation (16), at least one of the insert openings (26) does not accommodate a carrier element (24) and/or, for absorbing radiation (16), at least one of the insert openings (26) accommodates a dummy carrier element (24’) which does not carry a mirror element (23).

Description

Radiation absorbing mirror device and lithography system

The invention relates to a mirror device, in particular a mirror device for a lithography system, comprising: a plurality of mirror elements for reflecting radiation; a plurality of carrier elements, each of which carries one of the mirror elements; and a mounting device having insertion openings formed in each case to accommodate one opposite of the carrier elements, wherein the plurality of carrier elements, each of which carries one of the carrier elements, are accommodated in a plurality of insertion openings of the mounting device. The invention also relates to a lithography system having at least one such mirror device.

The lithography system may be a lithography apparatus for exposing wafers or some other optical device for lithography, such as an inspection system, for example for inspecting masks, wafers, (mirror) components used in lithography, etc. The lithography system may be embodied for EUV lithography, for example in the form of an EUV lithography apparatus, which is used for producing semiconductor components and operates with short-wavelength radiation (so-called EUV radiation), with an operating wavelength between about 5 nm and 30 nm.

Heat is generated in lithography systems, in particular EUV lithography equipment, inter alia due to absorption of EUV radiation, heating of optical elements in the form of mirrors, due to friction losses during movement of actuators, etc. The heat generated during operation of the lithography system can be dissipated by cooling components of the lithography system.

By way of example, the component to be cooled may be a mirror element in the form of a micromirror array, in particular a microelectromechanical mirror module ("MEMS mirror module"). A MEMS mirror module has a plurality of micromirrors arranged in a grid, which can usually be actuated or tilted about at least one axis, preferably about two axes. In each case, the micromirrors are very small components (e.g., dimensions corresponding to the mirror surface of approximately 1 mm ² ) and are controlled or actuated by means of logic elements and micromechanical structures in chip format. The actuation of the micromirrors of the corresponding mirror module is accompanied by the release of heat, which is difficult to dissipate due to the small size of the micromirrors or the way they are mounted.

Patent document DE 10 2013 205 214 B4 describes a micromechanical or microelectromechanical tool for a projection exposure apparatus, comprising at least one micromechanical or microelectromechanical component and a temperature control device with a gas supply device and a gas suction member. The at least one micromechanical or microelectromechanical component is encapsulated in a housing having a gas supply line and a gas exhaust line and at least one window for a working light of the projection exposure apparatus. Specifically, the tool can be a multi-mirror device having a plurality of electromechanical micromirrors.

Patent document DE 10 2014 219 770 A1 describes a mirror device, comprising: at least one mirror element, which carries a mirror surface arranged to reflect electromagnetic radiation; at least one carrier element, which comprises a head and a seat arranged to accommodate the at least one mirror element; and a mounting device for accommodating the at least one carrier element. At least one insertion opening is formed in the mounting device, and the seat of the carrier element is immersed in the insertion opening. A channel device for guiding a heat carrier medium is formed in the mounting device in the seat area. A local channel system (heat pipe) that can be formed in the carrier element is embodied to assist the heat transfer from the head area to the seat area, in combination with a phase change of the heat carrier medium introduced into this local channel system of the carrier element. For example, each of the mirror elements may form a mirror array.

The mirror arrangement described above can be used, for example, in an illumination system of a lithography device for illuminating an object field provided with a mask. This illumination system can be designed such that only two mirror arrangements with a plurality of micromirror elements are required. In this case, a first mirror arrangement in the beam path can be designed as a field-forming element in the form of a mirror reflector, and a second mirror arrangement in the beam path can be used to image the mirror reflector into the exit pupil of the illumination system, as described, for example, in patent document DE 10317667 A1. In particular, the first and second mirror arrangements can be designed as faceted mirrors.

Compared to illumination systems with at least three mirror arrangements, the illumination system described in DE 10317667 A1 has the advantage of improved transmission and thus higher productivity of the lithography system. In order to produce certain illumination settings, it is particularly in the case of such an illumination system that it does not contribute to the system performance if light reflected by the mirror elements in the first mirror arrangement reaches the object field of the illumination system.

In principle, a beam dump providing unwanted radiation can be used to absorb light or radiation. For this purpose, patent document DE 10 2015 210 041 A1 proposes at least one thin layer arrangement using at least one reflecting thin layer. The thin layer arrangement is configured such that reflected light is directed toward the at least one beam dump, which is incident at least intermittently on the thin layer arrangement during operation of the projection exposure apparatus and does not belong to the light pipe used.

The object of the present invention is to provide a mirror device which absorbs unwanted radiation and in the process minimizes the effect on the optical properties of the mirror device. Another object of the present invention is to provide a lithography system, in particular a lithography device, having at least one such mirror device. Subject of the invention

According to a first aspect, the object is achieved by a reflector device of the aforementioned type, wherein, for absorbing incident radiation, at least one insertion opening does not accommodate a carrier element (and also does not accommodate a dummy carrier element), and/or wherein, for absorbing incident radiation, at least one of the insertion openings accommodates a dummy carrier element that does not carry a reflector element.

Thus, the number of insertion openings in the mirror device according to the invention is greater than the number of carrier elements to which mirror elements are attached, which are inserted into these insertion openings. At least one insertion opening which does not accommodate a carrier element can be used as a beam dump and/or at least one dummy carrier element which does not carry a mirror element can be used as a beam dump. The dummy carrier element which does not carry a mirror element usually has a seat which is immersed in the insertion opening and is formed in the same or similar manner as the seat of the carrier element which carries the mirror element. In practice, the number of beam dumps, i.e. the number of insertion openings without carrier elements or the number of dummy carrier elements which do not carry a mirror element, can be specified as required within the production range of the mirror device, depending on how much power is to be consumed. Additionally, since the carrier element is usually detachably connected to the mounting device, the number of beam dumps can be selectively changed after the mirror device has been produced. Thus, individual carrier elements can be removed or a carrier element carrying a mirror element can be replaced by a dummy carrier element that does not carry any mirror element.

As already mentioned above, a dedicated component in the form of a beam dump which is thermally decoupled from the mirror arrangement can in principle be used to absorb radiation. However, it is not possible in all cases to absorb radiation by means of a separate component which is a beam dump, since the radiation to be absorbed needs to be directed to the beam dump. In the case where the mirror arrangement according to the invention is a second mirror arrangement of an illumination system, which is intended to absorb some of the radiation emitted from the first mirror arrangement of the illumination system so that it does not reach the reticle or the object field, it is problematic that the mirror elements in the first mirror arrangement, which are usually in the form of micromirrors, can only be tilted by a relatively small angle when actuated. This has the result that it is generally not possible to direct the unwanted radiation emitted from the first mirror arrangement to a separate beam dump which is thermally decoupled from the second mirror arrangement. Such a beam dump cannot be achieved due to the limited switching range of the mirror element in the first mirror arrangement. In order to direct the unwanted radiation to the beam dump, the switching range or the angle over which the mirror element in the first mirror arrangement can be tilted must be increased; this is very problematic from a manufacturing point of view.

In order to be able to absorb unwanted radiation, despite the limited switching range of the mirror element in the first mirror device, it is advantageous to place a beam dump on the mounting device of the second mirror device, in the vicinity of the mirror element in the second mirror device. However, this device heats up at the location of the beam dump and thus has the risk of thermoelastic deformation. This would reduce the positioning accuracy of the mirror element in the second mirror device, where the purpose is to reflect the incident radiation; as a result, the mirror element no longer hits exactly at the intended location on the reticle or thermally drifts.

The reflector device according to the invention allows incident radiation to be absorbed without significantly affecting the optical properties of the reflector device in the process: the absorbed radiation can be effectively absorbed and dissipated at the insertion opening or at a dummy carrier element accommodated in the insertion opening, so as to prevent significant heating of the mounting device and thus thermal drift behavior of the reflector element.

For cooling the insertion opening as beam dump or for cooling the virtual carrier element as beam dump, known concepts related to cooling mirror elements can be used, for example as described in the previously cited patent document DE 10 2014 219 770 A1, the content of which is incorporated by reference in its entirety into the content of the present invention. In the case of the above-mentioned mirror device, components already present in the mirror device can be used to implement the beam dump. Therefore, it is not necessary to newly develop or produce a beam dump and the associated cooling concepts for the beam dump. In particular, one and the same cooling device or one and the same cooling system can be used to cool the mirror element as beam dump and the insertion opening and/or the virtual carrier element as beam dump. In this way, the heat of the mount can be kept very low in the region of the beam dump (of the same order of magnitude as the mirror element integrated there). Furthermore, an effective cooling system can be implemented and thus thermal deformations of the mount can be reduced, thereby preventing thermal drift behavior of the mirror element.

In one embodiment, the mirror device comprises at least one channel device for guiding the coolant and is formed in the region of at least one insertion opening in the mounting device that does not accommodate the carrier element and/or in the region of the bottom of at least one dummy carrier element. With the aid of the channel device, heat can be effectively dissipated from the insertion opening and/or the dummy carrier element as a beam dump. The temperature of the coolant guided through the channel device can be adjusted so that it corresponds essentially to a target temperature of the mirror device. For example, the channel device can be implemented in the manner described in patent document DE 10 2014 219 770 A1 for cooling the corresponding mirror element. As described therein, the corresponding carrier element usually has a seat that is immersed in the insertion opening. However, in contrast to the carrier element described therein, no mirror element is attached to the head of the virtual carrier element acting as a beam dump; instead, the head acts as a beam dump for absorbing radiation.

In a further embodiment, the inner wall of the at least one insertion opening is formed by a socket element embedded in the mounting device, preferably, the channel means for guiding the coolant is formed at least partially by a cutout extending in an outer region of the socket element.

As described in patent document DE 10 2014 219 770 A1, the channel means for guiding the coolant can be provided at least partially through a cutout extending in the outer area of the socket element, which cutout is, for example, in the form of a hollow cone. Alternatively or additionally, a groove or a channel structure can also be formed, which is arranged to guide the coolant in the main body forming the mounting device. The coolant can also be guided via a channel means directly formed in the mounting device or via a channel system connected to a channel means arranged on part of the socket element. The channel means or the channel system for guiding the coolant can also extend only in the main body of the mounting device, without the need for a socket element. For example, if the mounting device or its main body is produced by layer manufacturing (for example using a 3D printing method), the socket element can be omitted. The channel system formed in the mounting device can be designed so that the surrounding area of multiple insertion openings is caused to be cooled in parallel. In particular, the channel system can be used to cool the surrounding environment of all insertion openings, that is to say, the insertion openings in which the reflector element is inserted and the insertion openings in which the carrier element is not inserted or the dummy carrier element is accommodated.

In a further embodiment, at least one inner wall of the insertion opening which does not accommodate a carrier element has a radiation absorbing coating and/or a radiation absorbing surface structure. If no carrier element is accommodated in the insertion opening, the radiation which is not desired to be reflected by the reflector device is substantially incident on the inner wall of the insertion opening, where it should be absorbed as effectively as possible. In principle, almost any material absorbs EUV radiation; i.e., an absorbing coating or an absorbing surface structure on the inner side of the insertion opening does not necessarily need to be used to absorb EUV radiation. However, the radiation incident on the reflector device or the beam dump may also have a wavelength longer than the EUV wavelength range, for example a wavelength radiation range in the wavelength range of EUV, UV, VIS or IR. Specifically, the wavelength of the radiation component generated by the EUV light source can be outside the EUV wavelength range and should not be propagated in the lithography system.

Radiation in these wavelength ranges can be absorbed effectively in particular by providing a radiation-absorbing coating and/or a radiation-absorbing surface structure, for example in the form of a suitably formed microstructure. As described above, the inner wall of the insertion opening can be formed by a socket element, the inner side of which is provided with an absorbing coating or an absorbing surface structure; however, this is not mandatory, that is, the inner wall of the insertion opening can also be formed directly on the mounting device.

In another embodiment, at least one insertion opening that does not accommodate a carrier element is hermetically sealed, preferably at a distance from one end of the reflector element. As described in patent document DE 10 2014 219 770 A1, a corresponding carrier element is usually inserted into the socket element in a sealed (hermetic) manner to hermetic seal the insertion opening. In this way, a vacuum can be applied to the side of the reflector device that is provided with the reflector element, without causing gas to flow into the rear area of the mounting device, wherein a vacuum is usually not applied via the joint area of the carrier element. If a carrier element is not accommodated in the insertion opening, the hermetic sealing of the insertion opening is advantageous for the same reason. For example, this can be achieved by inserting a seal in the form of a plug in the above-mentioned socket element, or by using a socket element with a can-shaped structure and a base for hermetic sealing of the insertion opening.

Generally, it is advantageous to hermetically seal the insertion opening on the side remote from the reflector element, rather than on the side located at the reflector element, in order to be able to utilize the largest possible area of the inner wall of the insertion opening as a beam dump. Specifically, radiation components that are incident on the inner wall for the first time and are not absorbed but are not desired to be reflected can also be reflected multiple times in the insertion opening and incident on the inner wall again, so that the radiation components are completely absorbed.

In a further embodiment, at least one virtual carrier element has a head region which protrudes beyond the insertion opening, the head region preferably protruding further beyond the insertion opening than the head region of the carrier element carrying the mirror element. Typically, the mirror element has a block-shaped or cuboid-shaped structure. In particular if the mirror element is a MEMS mirror module (see below), its thickness cannot be ignored, since in addition to the tiltable micromirrors, the control logic must also be incorporated in the mirror element. Therefore, for efficient absorption of radiation by the virtual carrier element, it is advantageous if the head region in the case of the virtual carrier element protrudes further beyond the insertion opening than in the case of those carrier elements carrying the mirror element. In particular, the head region or its end surface may protrude beyond the insertion opening until the head region or its end surface is approximately flush with the top end of the reflector element (in a non-tilted position).

In a further embodiment, the virtual carrier element has an absorbing coating and/or an absorbing surface structure on a head region protruding beyond the insertion opening, in particular on the end faces of the head region. As described above, this is particularly advantageous for absorbing incident radiation in a wavelength range longer than the EUV wavelength range. If the virtual carrier element is accommodated in the insertion opening, the virtual carrier element typically has a head region protruding beyond the insertion opening and a large part of the radiation absorbed by the virtual carrier element is intended to be incident on this head region. The absorbing coating and/or the absorbing surface structure can be provided on the protruding head region, in particular on its end faces; however, this is not mandatory.

In a further embodiment, at least one virtual carrier element has a solid structure at least in the head region, in particular in the entire head region. Effective heat dissipation can be ensured by the solid structure of the virtual carrier element. In contrast, the carrier element carrying the mirror element usually has through-channels for guiding connection lines and control lines through the carrier element in order to connect the plurality of actuators included in the mirror element to an electronic actuation system.

In one development, a closed channel system with an introduced coolant is formed in the virtual carrier element, wherein the coolant preferably cooperates with a phase change so that heat is transferred from the head area of the virtual carrier element to the bottom. The coolant in the closed channel system, which may be present in the form of water, for example, can absorb heat without changing its phase. The closed channel system with the introduced coolant, in this case in cooperation with the phase change, can transfer heat from the head area of the virtual carrier element to the bottom, for example based on the principle of a heat pipe.

In an alternative development, the virtual carrier element has a channel system for guiding the coolant, which channel system includes an inlet for the coolant and an outlet for the coolant. In contrast to the embodiment described further above, the channel system is not closed in this case, that is, the virtual carrier element is directly cooled. In this way, the heat path from the heat source (the surface on which the radiation is incident) to the coolant can be reduced or kept as short as possible. Typically, the channel system of the virtual carrier element is designed to supply the coolant to the head region of the virtual carrier element and to discharge the coolant from the head region of the virtual carrier element.

In a development of this embodiment, the reflector device is designed to connect the inlet and outlet fluids of the channel system in a sealing manner to the channel device of the mounting device or to the channel device of a heat sink arranged adjacent to the mounting device.

In the first case described further above, the mounting device has a channel device comprising a supply opening for supplying coolant to the inlet and a discharge opening for discharging coolant from the outlet of the channel system of the virtual carrier element. For example, if the inlet and outlet of the channel system are formed at the bottom of the carrier element, the sealing between the virtual carrier element and the channel device of the mounting device is implemented by radial sealing elements, or, if the inlet and outlet are arranged in the head region of the carrier element and have a lateral offset to the insertion opening, by means of axial sealing means.

In the second case described further above, the inlet and outlet are directly connected to the channel means of the heat sink arranged adjacent to the mounting device and are usually not fluid-tightly connected to the channel means of the mounting device. The fluid-tight connection of the inlet and outlet of the virtual carrier element to the channel means of the heat sink can be implemented by means of a sealing device. For example, the sealing device can be designed as an axial or radial seal.

In an alternative, the inlet and outlet of the dummy carrier element may be connected via lines (eg via tubes) to an external cooling device or an external cooling circuit to enable direct cooling.

As described in patent document DE 10 2014 219 770 A1, the (virtual) carrier element is preferably geometrically adapted so as to provide a cross-section that is sufficient for heat transfer and as large as possible, at least in the bottom of the immersion mounting. Preferably, a material with good thermal conductivity and moderate thermal expansion, preferably as small as possible, is selected for the carrier element. For example, copper, silicon, silicon carbide (SiC), molybdenum alloys, tungsten alloys or stainless steel are problematic as materials. The shape of the bottom of the carrier element and the inner wall of the insertion opening is preferably conical or pyramidal; however, this is not mandatory, for example, the bottom of the carrier element and the inner wall of the insertion opening can also be cylindrical in form.

For example, the coolant may be water, an aqueous mixture, ethylene glycol, a gas or gas mixture or liquid CO ₂ , wherein a phase change from liquid to gas may be utilized in the gaseous state, such as described above in a heat pipe.

In another embodiment, the mirror element is in the form of a MEMS mirror module. A MEMS mirror module has a plurality of micro-electromechanically actuatable micro-mirrors, typically arranged in a grid (array). As described above, each micro-mirror can be actuatable individually and can typically be tilted about at least one axis, typically about two axes. The number of micro-mirrors in a MEMS mirror module may vary; for example, 24×24 or 25×25 micro-mirrors can be arranged in a grid. The corresponding MEMS mirror module typically also includes logic elements and micromechanical structures in wafer form to control or actuate the micro-mirrors.

In a further embodiment, a plurality of mirror elements are arranged in a grid, at least one insertion opening which does not accommodate a carrier element and/or at least one insertion opening which accommodates a dummy carrier element being arranged at a side edge of the grid or between the mirror elements of the grid, in particular in the center of the grid. As described above, it is advantageous if the insertion opening used as a beam dump or the carrier element used as a beam dump is arranged as close as possible to the mirror element in the mirror device. Because this means that there is no need to increase the switching range of the mirror elements of another mirror device arranged upstream of the beam path in order to guide the radiation reflected there to the corresponding beam dump of the mirror device according to the invention. The beam dump at the side edge of the grid is located at the outermost position of the corresponding row and/or column of the grid. A beam dump at the edge of the grid is also understood to mean a beam dump which is placed next to a beam dump arranged at the outermost position. As an alternative or in addition to configuring the beam dump at the side edge of the grid, the beam dump can also be arranged in such a way that it is distributed between the mirror elements of the grid, that is to say not at the edge of the grid but, for example, in the center or middle of the grid.

In the cooling concept described above, the corresponding carrier element carrying the mirror element or acting as a beam dump can be replaced without having to open or interrupt the cooling circuit in the process.

The fixing section corresponding to the carrier element can be used to fix the (virtual) carrier element to the mounting device, and the holding force that fixes the carrier element in the mounting device is introduced into the carrier element via the fixing section. For example, the fixing section can be in the form of a threaded section, on which a nut is arranged, which generates the holding force in the locked state. The holding force generated by the nut can be transmitted to the mounting device, for example, by including a spring. A pressing mechanism that presses the carrier element "from below" out of the mounting device can also be positioned in the region of the fixing section.

Another aspect of the invention relates to a lithography system, in particular a lithography apparatus, comprising: at least one mirror device as further described above, wherein the mirror device is preferably arranged in an illumination system of the lithography apparatus. The lithography system may be a lithography apparatus for exposing a wafer or some other optical device for lithography, such as an inspection system, for example for inspecting lithography apparatus, wafers, etc. used in lithography. The lithography system may in particular be an EUV lithography system, which is designed to use wavelength radiation in the EUV wavelength range, which has a wavelength range between 5 nm and 30 nm.

The illumination system can have exactly two mirror arrangements, wherein the first mirror arrangement in the beam path forms a mirror reflector, as described in the previously cited patent document DE 10317667 A1, the content of which is hereby incorporated by reference in its entirety into the present invention. The illumination system can also have a different structure and, for example, have three or more mirror arrangements. In particular, the mirror arrangement can be in the form of a faceted mirror.

In one embodiment, the lithography system comprises a further mirror device having a plurality of further mirror elements, wherein the further mirror device is arranged in the illumination system in the beam path upstream of the mirror device, and the plurality of further mirror elements are designed to radiate radiation to be absorbed at at least one insertion opening that does not accommodate a carrier element and/or at at least one insertion opening that accommodates a dummy carrier element. Furthermore, the further mirror device is designed to radiate radiation to be reflected at the mirror elements of the mirror device so as to radiate it to the object field or the mask. For example, the further mirror elements of the further mirror device can be MEMS mirror modules.

As described above, in this case, it is advantageous if the mirror element and the insertion opening serving as a beam dump or the virtual carrier element are arranged as adjacent to one another as possible so that further mirror elements in further mirror arrangements do not need to be tilted too far in order to direct the radiation to be absorbed to the insertion opening serving as a beam dump or to the virtual carrier element of the mirror arrangement according to the invention.

From the following description of the working examples of the present invention, with reference to the accompanying drawings showing important details of the present invention and the scope of the patent application, further features and advantages of the present invention will become clear. In the variants of the present invention, each feature can be implemented alone or in any combination with its own rights.

Essential parts of an optical device for EUV lithography in the form of a lithography projection exposure apparatus 1 (EUV lithography apparatus) are described below by way of example with reference to Fig. 1. The description of the basic structure of the projection exposure apparatus 1 and its components should not be considered limiting here.

An embodiment of an illumination system 2 of a projection exposure apparatus 1 has a light or radiation source 3 and an illumination optical unit 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be arranged as a module separate from the rest of the illumination system. In this case, the illumination system does not contain the light source 3.

A reticle 7 arranged in the object field 5 is illuminated. The reticle 7 is held by a reticle carrier 8. The reticle carrier 8 can be moved by a reticle displacement driver 9, in particular in a scanning direction.

For explanation purposes, a Cartesian xyz coordinate system is depicted in FIG1 . The x direction is perpendicular to the drawing plane. The y direction extends horizontally and the z direction extends vertically. The scanning direction extends along the y direction in FIG1 . The z direction extends perpendicular to the object plane 6 .

The projection exposure apparatus 1 comprises a projection system 10. The projection system 10 is used to image the object field 5 into an image field 11 in an imaging plane 12. The structures on the mask 7 are imaged onto a light-sensitive layer of a wafer 13 arranged in the region of the image field 11 in the imaging plane 12. The wafer 13 is held by a wafer carrier 14. The wafer carrier 14 can be moved by a wafer displacement driver 15, in particular in the y direction. On the one hand, the mask 7 is moved by the mask displacement driver 9 and on the other hand, the wafer 13 can be moved synchronously by the wafer displacement driver 15.

A radiation source 3 is an EUV radiation source. In particular, the radiation source 3 emits EUV radiation 16, hereinafter also referred to as used radiation, illumination radiation or illumination light. In particular, the used radiation has a wavelength range between 5 nm and 30 nm. The radiation source 3 may be a plasma source, such as a laser induced plasma (LPP) source or a gas discharge induced plasma (GDPP) source. It may also be a synchronization-based radiation source. The radiation source 3 may be a free electron laser (FEL).

The illuminating radiation 16 emitted from the radiation source 3 is focused by a condenser 17. The condenser 17 can be a condenser with one or more elliptical and/or hyperbolic reflecting surfaces. The illuminating radiation 16 can be incident on at least one reflecting surface of the condenser 17 with grazing incidence (GI), that is to say with an angle of incidence greater than 45°, or with normal incidence (NI), that is to say with an angle of incidence less than 45°. The condenser 17 can be structured and/or coated, firstly in order to optimize its reflectivity for the radiation used and secondly in order to suppress extraneous light.

The illumination radiation 16 propagates through an intermediate focus in an intermediate focus plane 18 downstream of the condenser 17. The intermediate focus plane 18 may constitute a separation between the radiation source module comprising the radiation source 3 and the condenser 17 and the illumination optical unit 4.

The illumination optical unit 4 comprises a deflection mirror 19 and a first faceted reflector 20 arranged downstream thereof in the beam path. The deflection mirror 19 can be a plane deflection mirror or, alternatively, a reflector having a beam influencing effect that goes beyond a pure deflection effect. Alternatively or additionally, the deflection mirror 19 can be in the form of a spectral filter, which separates the used light wavelength of the illumination radiation 16 from extraneous light deviating from its wavelength. The first faceted reflector 20 comprises a plurality of individual first facets 21, which are also referred to as field facets hereinafter. FIG. 1 only depicts some of the facets 21 by way of example. In the beam path of the illumination optical unit 4, a second faceted reflector 22 is arranged downstream of the first faceted reflector 20. The second facet reflector 22 includes a plurality of second facets 23 .

The illumination optical unit 4 thus forms a double-faceted system. This basic principle is also referred to as a compound eye integrator. The individual first facets 21 are imaged into the object field 5 by means of a second facet mirror 22. The second facet mirror 22 is the last beam shaper or, in fact, the last mirror of the illuminating radiation 16 in the beam path upstream of the object field 5.

The projection system 10 includes a plurality of reflection mirrors Mi, which are numbered consecutively according to their configuration in the beam path of the projection exposure apparatus 1.

In the example shown in FIG. 1 , the projection system 10 comprises six mirrors M1 to M6. Alternative examples with 4, 8, 10, 12 or any other number of mirrors Mi are also possible. The penultimate mirror M5 and the last mirror M6 each have a through hole for irradiating radiation 16. The projection system 10 is a double-shading optical unit. The image-side numerical aperture of the projection optical unit 10 is greater than 0.4 or 0.5, and may also be greater than 0.6, for example, 0.7 or 0.75.

Like the reflector of the illumination optical unit 4 , the reflector Mi can have a highly reflective coating for the illumination radiation 16 .

Fig. 2 shows a partial cross-sectional view of a second mirror device 22 in the form of a faceted mirror of the illumination system 2 of Fig. 1. The mirror device 22 has a plurality of mirror elements 23 which are arranged in close proximity, form a concave surface and are aligned relative to the optical center. Each mirror element 23 is used to reflect electromagnetic radiation, more precisely EUV radiation 16, which is EUV radiation reflected from the facet 21 of the first faceted mirror 20 in the illumination system 2 to the mirror device 22 in the form of a second faceted mirror. In the example shown, the mirror element 23 is in the form of a MEMS mirror module. The corresponding MEMS mirror module has a plurality of micromirrors which are arranged in a grid (e.g. with 25×25 micromirrors) and can be actuated on an individual basis for more precise tilting. For this purpose, the corresponding mirror element 23 in the form of a MEMS mirror module has logic elements and micromechanical structures in the form of a chip.

The reflector device 22 shown in FIG. 2 also comprises a plurality of carrier elements 24, each carrying one of the reflector elements 23. The reflector device 22 also has a mounting device 25, which comprises a conical insertion opening 26, which is designed to accommodate a corresponding one of the conical carrier elements 24, each of which carries a corresponding reflector element 23. The mounting device 25 has a multi-part structure and has a plurality of frame shells assembled together in a layered manner. For details on the structure of the reflector device 22, how the carrier element 24 is fastened to the mounting device 25 and the structure of the mounting device 25, please refer to patent document DE 10 2014 219 770 A1.

FIG. 3 shows a plan view of a mirror element 23 of the mirror arrangement 22 of FIG. 2 , more precisely its reflective surface or end face, which in the example shown has a square geometry. It will be appreciated that the mirror element 23 can also have a different geometry. It is also clear from FIG. 3 that the mirror elements 23 are arranged in a grid 27 having a plurality of rows and columns. Each grid position shown in dashed lines in FIG. 3 also has an insertion opening 26 but no mirror element 23 is arranged thereon, which can be identified at the side edges 27 a of the grid 27. The grid positions at the edges of the grid 27 shown in FIG. 3 are used for beam dumps that absorb EUV radiation 16, which is reflected by the facets 21 in the first facet mirror 20 to the mirror arrangement in the form of the second facet mirror 22, but should not reach the mask 7. In the case of certain lighting settings or operating states of the lighting system 2, radiation 16 reflected by certain facets 21 of the first facet reflector 20 at corresponding angular positions which are advantageously provided for this purpose is captured or absorbed.

Providing a beam dump at the side edges 27a of the grid 27 of the mirror element 23 is advantageous because the facets 21 in the first facet mirror 20 can be actuated (usually tilted), but the tilt angle that can be set during actuation is relatively small. Generally, it is therefore not possible to direct unwanted radiation 16 emanating from the facets 21 in the first facet mirror 20 to a beam dump arranged next to the second facet mirror 22. However, the switching range of the facets 21 in the first facet mirror 20 is sufficient to direct unwanted radiation to the left edge 27a and the right edge 27b of the grid 27 of the mirror element 23 in order to absorb radiation 16 incident thereon. Alternatively or additionally to the arrangement of the beam dump at the side edges 27a, 27b of the grid 27, the beam dump can also be arranged in a distributed manner between the mirror elements 23 of the grid, for example in the center 27c of the grid 27, as shown in FIG.

In order to avoid a situation where the mounting device 25 is deformed during absorption of radiation 16 and the mirror element 23 no longer deflects the incident radiation 16 to the desired location on the reticle 7, it is necessary to effectively cool the mounting device 25 at the grid locations for absorbing radiation 16. Two options for effective cooling or heat dissipation are described below in conjunction with Figures 4a and 4b.

FIG. 4a shows a beam dump in the form of an insertion opening 26 without a carrier element 24 and two adjacent insertion openings 26, each of which accommodates a carrier element 24 carrying a reflector element 23. As can be seen from FIG. 4a, the radiation 16 to be absorbed enters the insertion opening 26 at the side of the mounting device 25 facing the reflector element 23 and is reflected multiple times at the inner wall 26a of the insertion opening 26, where most of the radiation 16 to be absorbed is absorbed. The geometry of the inner wall 26a of the insertion opening 26 does not need to be conical as shown in FIG. 4a; rather, it can be cylindrical or any other geometric shape as shown in FIG.

In the example shown, the inner wall 26a of the insertion opening 26 has an absorbing coating 28 for absorbing the incident radiation 16. Alternatively or additionally, the inner wall 26a of the insertion opening 26 has an absorbing surface structure. In the example shown, the absorbing coating 28 is designed to absorb radiation with a wavelength longer than 30 nm generated by the light source 3, such as radiation in the VUV, UV, VIS or IR wavelength range. Even without the absorbing coating 28 or the surface structure, the material of the inner wall 26a of the insertion opening 26 will absorb a significant portion of the incident radiation 16 with a wavelength in the EUV wavelength range.

According to Kirchhoff's law for thermal radiation, the following formulas apply for the emissivity ε (in this case, the absorption of incident radiation by the beam dump due to absorption), the reflection δ and the transmission τ (in each case in %): ε + δ + τ = 1. All three parameters depend on the wavelength and the angle of incidence of the incident radiation 16, and this dependence is neglected in the following considerations to simplify the situation. The effective emissivity εeff of the beam dump for the incident radiation 16 (corresponding to the effective absorption of the beam dump) depends not only on the emissivity ε of the beam dump in the case of the corresponding reflection at the inner wall 26a, but also on the number of reflections n at the inner wall 26a. In this case, the effective emissivity εeff of the beam dump should be as close to 1 as possible, so that the radiation 16 falling into the beam dump is converted as completely as possible into heat, which can be removed by a cooling device.

The effective emissivity εeff of the beam dump can be estimated according to the following formula: εeff = 1 – (1 -ε)n. In this formula, the effect of the angle of incidence is neglected and the transmittance τ = 0 is assumed. For example, if the emissivity ε of the beam dump for the entire incident radiation 16 (averaged over the radiation in the EUV wavelength range and other wavelength ranges) is assumed to be about 35% in the case of reflection at the inner wall 26a, and if n=3 reflections are assumed, then the effective emissivity is as follows: εeff = 72.5%. As described above, in this case the emissivity ε is averaged over all wavelengths of the incident radiation 16. The emissivity ε of the incident radiation 16 in the EUV wavelength range and the effective emissivity εeff of the beam dump are significantly higher than the values calculated here.

In order to effectively dissipate the absorbed radiation 16, the mounting device 25 has a channel means 29 in the form of a channel system for guiding a coolant 30, which in the example shown here is cooling water. Alternatively, other coolants can also be used, such as aqueous mixtures, glycols, gases or gas mixtures or (liquid) _CO2 . In the example shown in FIG. 4a, the inner wall 26a of the insertion opening 26 is formed by a socket element 31 embedded in the mounting device 25. In the example shown, the formation of the channel means 29 for guiding the coolant 30 is achieved at least partially by a cutout 29a extending in the outer area of the socket element 31. For details on the design of the channel arrangement 29 and the interaction with the socket element 31, reference is made to patent document DE 10 2014 219 770 A1.

At the end of the conical socket element 31 remote from the reflector element 23, the seat 31a hermetically seals the insertion opening 26. This allows a vacuum to be applied to the side of the reflector device 22 on which the reflector element 23 is arranged, in the process of which the air flow from the rear region of the mounting device 25 cannot reach the front side of the reflector device 22 through the insertion opening 26. In an alternative to the solution shown in FIG. 4a, a seal in the form of a plug or the like can be used to hermetically seal the insertion opening 26. The carrier element 24 is also inserted into the corresponding socket element 31 in order to seal the socket element 31. An O-ring 32 is inserted into a corresponding annular groove in the carrier element 24 to achieve sealing through a seal in the form of an O-ring 32.

Fig. 4b shows a diagram similar to Fig. 4a, wherein the beam dump is realized by a virtual carrier element 24' which, in contrast to the two other carrier elements 24 shown in Fig. 4b, does not carry a mirror element 23. The virtual carrier element 24' used as beam dump has a base 33 protruding into the insertion opening 26 and a head region 34' which protrudes beyond the insertion opening 26 in the direction of the mirror element 23. The head region 34' protrudes further beyond the insertion opening 26 than the head region 34 of an adjacent carrier element 24, each of which carries a mirror element 23. The further protruding head region 34' has an end face 35 which terminates flush with the end face or reflecting surface of the adjacent mirror element 23. This and the provision of an absorbing surface structure 36 on the end face 35 of the head region 34' allow radiation 16 incident on the head region 34' of the dummy carrier element 24' to be effectively absorbed. The absorption of the incident radiation 16 at the end face 35 of the head region 34' should be greater than 70%.

In order to effectively dissipate the heat absorbed from the head region 34' of the virtual carrier element 24', a closed channel system 37 with an introduced coolant 38 is formed in the virtual carrier element 24', more precisely in the seat 33, which coolant cooperates with the phase change so that the heat is transferred from the head region 34' to the bottom 33 of the virtual carrier element 24' (the so-called heat pipe). For example, the coolant 38 can be CO _2. Alternatively, the coolant 38 in the closed channel system 37 may not change its phase. As can be seen from FIG. 4 b , the closed channel system 37 is limited to the bottom 33 of the virtual carrier element 24 ′; i.e., the head region 34 ′ of the virtual carrier element 24 ′ has a solid structure, but this is not mandatory. In contrast, the carrier element 24 carrying the mirror element 23 has a through channel 39 for guiding connection lines and control lines through the carrier element 24 to connect the actuator included in the mirror element to the electronic actuation system.

Unlike FIG. 4 b , the virtual carrier element 24 ′ can also have an entirely solid structure, that is to say without a cavity. In both cases, the virtual carrier element 24 ′ can be cooled in the manner described in the entire text of FIG. 4 a , that is to say by means of a channel arrangement 29 which is designed to guide the coolant 30 and is formed partly by cutouts 29 a extending in the outer region of the socket element 31. However, the use of a socket element 31 is not mandatory.

FIG. 4 c shows a diagram similar to FIG. 4 a , in which the beam dump is formed by an insertion opening 26 which does not accommodate the carrier element 24, which insertion opening is cylindrical in the example shown. In the reflector device 22 shown in FIG. 4 c , the mounting device 25 is produced by layered manufacturing using a 3-D printing method. The channel device 29 for guiding the coolant 30 has been introduced in the form of a cavity into the material of the mounting device 25 or its body during the production of the mounting device 25. The provision of the socket element 31 or the cutout 29 a can be omitted in the reflector device 22 shown in FIG. 4 c . It should be understood that the virtual carrier element 24 ′ described in FIG. 4 b can also be used as a beam dump in the case of the reflector device 22 shown in FIG. 4 c .

In an alternative to the exemplary embodiment described in FIG. 4 b , the channel system 37 ′ of the virtual carrier element 24 ′ may not be closed, but may have an inlet 40 for the coolant 38 and an outlet 41 for the coolant 38, as shown in FIGS. 5 a, b , each showing details of the mirror device 22. In the example shown in FIGS. 5 a, b , the channel system 37 ′ of the virtual carrier element 24 ′ is not fluidically connected to the channel device 29 of the mounting device 25 via the inlet 40 and the outlet 41.

In the example shown in FIG. 5 a , the coolant 38 is supplied to an inlet 40 formed on a fixing portion 42 of the virtual carrier element 24 ′, which protrudes beyond the insertion opening 26, is discharged from the external cooling device via a supply line (not shown here), and is discharged from an outlet 41 via a discharge line (not shown here) and conveyed to the external cooling device. The outlet 41 is also formed on a fixing portion 42 of the virtual carrier element 24 ′, which protrudes beyond the insertion opening 26.

In the example shown in FIG. 5 b , a heat sink 43 having a channel system 29 of a similar form to the channel system 29 of the mounting device 25 is arranged adjacent to the mounting device 25, the channel system being designed to supply coolant 38 to the inlet 40 of the virtual carrier element 24 ′ and to discharge the coolant from the outlet 41 of the virtual carrier element 24 ′. Thermal deformations of the mounting device 25 can be reduced by guiding the coolant 38 in the additional heat sink 43. In the case shown in FIG. 5 b , it is advantageous or necessary to seal the inlet 40 and the outlet 41 by means of seals (not shown here). Radial and/or axial sealing concepts can be used for this purpose. In the case of a suitable design of the corresponding seals, for example in the form of suitable adapters or the like, the dummy carrier element 24' can optionally be replaced without interrupting the delivery of the coolant 38 for this purpose. In particular, when the dummy carrier element 24' is fixed in the mounting device 25, a fluid-tight connection can be established between the inlet 40 and the outlet 41 and the channel device 29 of the heat sink 43.

Unlike shown in Fig. 5a, b, the inlet 40 and outlet 41 of the channel system 37' of the virtual carrier element 24' can also be connected in a fluid-tight manner to the channel means 29 of the mounting device 25. In this case, the inlet 40 and outlet 41 are not attached to the fixing part 42 of the virtual carrier element 24', but, for example, on the side of the bottom 33 of the virtual carrier element 24', relative to the inner side 26a of the insertion opening 26. In this case, the socket element 31 shown in Fig. 4b can be omitted. In this case, the supply opening of the channel means 29 of the mounting device 25 leads to the annular space formed between the virtual carrier element 24' and the inner side 26a of the insertion opening 26. In this case, the channel means 29 of the mounting means 25 also has a discharge opening for the coolant 38, which leads to the (further) annular space into which the outlet 41 of the virtual carrier element 24' leads. The annular space can be sealed by means of a radial seal, for example in the form of an O-ring or the like.

Alternatively, the inlet 40 and the outlet 41 of the channel means 37' of the virtual carrier element 24' can also be formed in the head region 34' of the virtual carrier element 24', more precisely, on the side of the end face of the head region 34' facing the mounting device 25, laterally offset from the insertion opening 26. In this case, the supply opening and the discharge opening of the channel means 29 of the mounting device 25 lead to corresponding gaps, into which the inlet 40 and the outlet 41 of the channel system 37' of the virtual carrier element 24' lead, respectively. In this case, the respective gap can be sealed from the surrounding environment by means of axial sealing means.

1: lithography system 2: illumination system 3: radiation source 4: illumination optical unit 5: object field 6: object plane 7: mask 8: mask carrier 9: mask displacement driver 10: projection system 11: image field 12: image plane 13: wafer 14: wafer carrier 15: wafer displacement driver 16: radiation 17: focusing lens 18: intermediate focal plane 19: polarizing lens 20: first facet reflector 21: first facet 22: reflector device 23: reflector element 24: carrier element 24': virtual carrier element 25: mounting device 26: insertion opening 26a: inner wall 27: grid 27a: side edge 27b: side edge 27c: center 28: absorbent coating 29: channel device 29a: cutout 30: coolant 31: socket element 31a: base 32: O-ring 33: seat 34: head area 34': head area 35: end face 36: absorbent surface structure 37: channel system 37': channel system 38: coolant 39: straight channel 40: inlet 41: outlet 42: fixing part 43: heat sink M1: reflector M2: reflector M3: reflector M4: Reflector M5: Reflector M6: Reflector

Exemplary embodiments are schematically illustrated in schematic diagrams and explained in the following embodiments; FIG. 1 shows a schematic longitudinal cross-sectional view of a projection exposure device for EUV projection lithography, the device having an illumination system with two faceted mirrors; FIG. 2 shows a perspective view of a mirror device in the form of a second faceted mirror of the illumination system of FIG. 1 ; FIG. 3 shows a schematic diagram of a plan view of a mirror element of the faceted mirror of FIG. 2 , the mirror element of the faceted mirror being configured as a grid, wherein a plurality of beam collectors for absorbing radiation are configured at the side edges and the center of the grid; FIG. 4a shows a schematic diagram of the mirror device of FIG. 3 , having a beam collector in the form of an insertion opening without providing a carrier element; FIG. 4b shows a schematic cross-sectional view of the mirror device of FIG. 3 with a beam dump in the form of a virtual carrier element without a mirror element; FIG. 4c shows a schematic cross-sectional view similar to FIG. 4a with a mounting device produced by 3D printing; FIG. 5a, b show schematic views of a virtual carrier element into which a channel system is introduced, the channel system having an inlet and an outlet for a coolant. In the following figure descriptions, the same figure reference numerals are used for components that are the same or have the same function.

16: Fallout

23: Reflector element

24: Carrier element

24’: Virtual carrier element

26: Insert opening

26a: Inner wall

28: Absorption coating

29a: Incision

30: Coolant

31: Socket components

31a: Base

32:O ring

33: Seat

34: Head area

34’: Head area

35: End face

36: Absorption surface structure

37: Channel system

38: Coolant

39: Direct access

Claims (15)

A mirror device (22), in particular for use in a lithography system (1), comprises: a plurality of mirror elements (23) for reflecting radiation (16); a plurality of carrier elements (24), each of which carries one of the mirror elements (23); a mounting device (25), having a plurality of insertion openings (26) for accommodating a corresponding one of the carrier elements (24), each of which carries one of the mirror elements (23), and the carrier elements (24) are accommodated in the insertion openings (26) of the mounting device (25); wherein, in order to absorb the radiation (16), at least one of the insertion openings (26) does not accommodate the carrier element (24); and/or In order to absorb the radiation (16), at least one of the insertion openings (26) accommodates a dummy carrier element (24'), which does not carry the carrier element (23). The reflector device as described in claim 1 also includes a channel device (29) for guiding a coolant (30), and the channel device (29) is formed in an area of at least one of the insertion openings (26) of the mounting device (25) that does not accommodate the carrier element (24) and/or a seat (33) of at least one of the virtual carrier elements (24'). A reflector device as described in claim 1 or 2, wherein an inner wall (26a) of at least one of the insertion openings (26) is formed by a socket element (31) embedded in the mounting device (25), and the channel device (29) for guiding the coolant (30) is preferably formed at least partially through a cutout (29a) extending in an outer area of the socket element (31). A reflector device as described in any of the preceding claims, wherein the inner wall (26a) of at least one of the insertion openings (26) that does not accommodate the carrier element (24) has a radiation (16) absorbing coating (28) and/or a radiation (16) absorbing surface structure. A reflector device as claimed in any of the preceding claims, wherein at least one of the insertion openings (26) not accommodating the carrier element (24) is hermetically sealed, preferably at an end remote from the reflector element (23). A reflector device as described in any of the preceding claims, wherein at least one of the virtual carrier elements (24') has a head area (34') protruding beyond the insertion opening (26) in the direction of the reflector element (23), and the head area (34') preferably protrudes further beyond the insertion opening (26) than the head area (34) of the carrier element (24) carrying the reflector element (23). A reflector device as claimed in any of the preceding claims, wherein the dummy carrier element (24') has an absorbing coating and/or an absorbing surface structure (36) on the head region (34') protruding beyond the insertion opening (26), in particular on the end face (35) of the dummy carrier element. A reflector device as described in claim 6 or 7, wherein at least one of the virtual carrier elements (24') has a solid structure at least in the head area (34'), in particular in the entire head area (34'). A reflector device as described in any one of claims 6 to 8, wherein a closed channel system (37) is formed in the virtual carrier element (24') and a coolant (38) is injected, preferably the coolant cooperates with the phase change to transfer heat from the head area (34') to the seat (33) of the carrier element (24'). A reflector device as described in any one of claims 1 to 8, wherein the virtual carrier element (24') has a channel system (37') for guiding the coolant (38), and the channel system includes an inlet (40) and an outlet (41) for the coolant (38). A reflector device as described in claim 10, wherein the inlet (40) and the outlet (41) of the channel system (37') are designed to be fluid-tightly connected to the channel device (29) of the mounting device (25), or to be fluid-tightly connected to a channel device of a heat sink adjacent to the mounting device (25). A mirror device as described in any of the preceding claims, wherein the mirror element (23) is in the form of a MEMS mirror module. A reflector device as described in any of the aforementioned claims, wherein the multiple reflector elements (23) are arranged to form a grid (27), wherein at least one of the insertion openings (26) that does not accommodate the carrier element (24) and/or at least one of the insertion openings (26) that accommodates the virtual carrier element (24') is arranged at the side edge (27a, 27b) of the grid (27) or between the reflector elements (23) of the grid (27), in particular in the center (27c) of the grid. A lithography system, in particular a lithography apparatus (1), comprises: at least one reflector device (22) as described in any of the preceding claims, preferably the reflector device (22) is arranged in an illumination system (2) for illuminating a mask (7). The lithography system as described in claim 14 further includes another reflector device (20) having a plurality of additional reflector elements (21), wherein the another reflector device (20) is arranged in the illumination system (2) in the beam path upstream of the reflector device (22), and the plurality of additional reflector elements (21) are designed to emit radiation (16), which is absorbed at at least one insertion opening (26) that does not accommodate a carrier element (24) and/or at least one insertion opening (26) that accommodates a dummy carrier element (24).

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